Albrecht schmidt



UNITED STATES PATENT OFFICE.

ALBRECHT SCHMIDT, OF BERLIN, GERMANY.

HYPOFELIMINATOR.

SPECIFICATION forming part of Letters Patent No. 530,965, dated December 18, 1894. Arrliwtion fileflJuly .189 Serial No. 516,995. (No specimens.)

To all whom it may concern:

Be it known that I, ALBRECHT SCHMIDT, a subject of the King of Prussia, residing at 170 and 171 Mullerstrasse, Berlin, Prussia, Germany, have invented certain new and useful Improvements in and Relating to the Removal of the Fixing Agent from Photo graphic Pictures; and I do hereby declare the following to be afull, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

My invention relates to the removal of the fixing agent-for instance of the hyposul phite of sodium-by treating the fixed pictures with persulphates.

Complaints are constantly heard of incomplete elutriation of the sodium fixing agent from photographic pictures and consequent discoloration of the photographs. Chloride of lime and eau de javelle which have been repeatedly recommended for destroying the last traces of the fixing agent, hyposulphite of sodium, and consequently shortening the elutriation process, have only been attended with slight success on account of their extremely inconstant composition. They have also other drawbacks.

Now I have found that the salts of persulphuric acid are excellently adapted for rendering an excess of hyposulphite harmless by oxidation. After the photograph has been fixed, the plate or paper is immersed in a dilute solutionof persulphate of potassium or of persulphate of ammonium or of persulphate of sodium. The formula of such a persulphate is represented by B 8 0 In this formula R stands for the radical, which may be potassium, sodium or ammonium. While otherwise it is necessary to wash for hours before the wash water no longer gives a yellow'precipitate with silver nitrate, the employment 0f persulphate effects the removal of all fixing agent in a far shorter time, and the subsequent discoloration of the plate is prevented.

Properly a one percent. solution of persulphate may be employed.

The solution must not be too much concentrated in order to avoid an oxidation of the silver. The solutions may also be made slightly alkaline. The efiect of slightly acid solutions is not so favorable.

Having thus described my invention and in what manner it is to be carried out, what I claim as new, and desire to secure by Letters Patent, is-

In the art of photography the improvement which consists in removing the fixing agent from photographic pictures by treating them 

